A polyrotaxane has a specific structure of having a cyclic molecule, and a straight-chain molecule threaded through the cyclic molecule in a skewered manner, and blocking groups arranged at both ends of the straight-chain molecule to prevent the cyclic molecule from being separated from the straight-chain molecule. In this polyrotaxane, the cyclic molecule can move on the straight-chain molecule relatively. Therefore, the polyrotaxane has various characteristics, particularly, excellent mechanical characteristics, and is expected to be applied and developed in various manners, and has also been used in an optical material such as a contact lens (see Patent literature 1), or the like. Meanwhile, in many optical materials, plastic lenses are used, and lighter in weight, harder to break and dyeable in comparison with inorganic lenses, and therefore have been widely used rapidly in every industrial field in recent years. One of the fields is a field of an eyeglass lens. The eyeglass lens is required to satisfy many functions such as transparency, excellent durability, easy dyeability, and resin strength enough to withstand processing, and various resin materials for lenses have been developed and used so far. Moreover, one of kinds of the eyeglass lenses is a photochromic eyeglass lens. The photochromic eyeglass lens means a material which is immediately colored in an outdoor place where the material is irradiated with light including ultraviolet rays such as sunlight to function as sunglasses, and in an indoor place where the material is not irradiated with such light, the material is faded to function as ordinary transparent eyeglasses. A demand therefor has increasingly grown in recent years.
In order to provide the optical material with photochromism, a photochromic compound is generally used in combination with a plastic material. Specifically, the following means are known: (a) a method for dissolving a photochromic compound into a polymerizable monomer, and polymerizing the resulting mixture to directly shape an optical material such as a lens, which method is called a kneading method; (b) a method for providing, on a surface of a plastic molded product such as a lens, a resin layer into which a photochromic compound is dispersed, by coating or cast polymerization, which method is called a lamination method; and (c) a method for bonding two optical sheets with an adhesive layer formed by an adhesive material resin into which a photochromic compound is dispersed, which method is called a binder method.
Incidentally, the optical material such as an optical article provided with the photochromism is further required to satisfy the characteristics as described below.
(I) A degree of coloring (initial coloring) in a visible light region before being irradiated with ultraviolet rays should be low.
(II) A degree of coloring (color optical density) upon being irradiated with ultraviolet rays should be high.
(III) A rate (color fading rate) from stopping irradiation with ultraviolet rays to return to an original state should be high.
(IV) Durability against repetitive reversible action of color development and color fading should be satisfactory.
(V) Storage stability should be high.
(VI) The optical material should be easily shaped into various shapes.
(VII) Photochromism should be provided without causing reduction of mechanical strength.
Accordingly, also upon producing the optical material having photochromism or the like by using the means (a) to (c) described above, various proposals have been made so that the requirements as described above may be satisfied. With regard to the color optical density, the color fading rate or the like, however, development of superb photochromism has been required in a current status.
For example, the kneading method described above has an advantage of capability of producing a photochromic plastic lens in bulk and at a low cost by using a glass mold, in which most of the photochromic plastic lenses are currently produced using this method.
In the kneading method, however, sufficient strength is required for a lens base material. Therefore, it is necessary to enhance mechanical strength of a matrix resin in which the photochromic compound is dispersed. Therefore, it becomes difficult to develop excellent photochromism. More specifically, a degree of freedom of molecules in the photochromic compound existing in the matrix resin is reduced, and therefore a photochromic reversible reaction is adversely affected.
With regard to such a kneading method, for example, Patent literature 2 describes a technique on adding a photochromic compound to a monomer composition containing an isocyanate monomer and a thiol monomer. Moreover, Patent literature 3 discloses a photochromic curable composition containing a specific (meth)acrylic polymerizable monomer and a photochromic compound.
Photochromic lenses shaped by allowing polymerization curing of these compositions, however, are unsatisfactory in view of photochromic characteristics, while the mechanical strength is high.
On the other hand, in the lamination method or the binder method, the photochromism is developed in a thinner layer formed on surfaces of various base materials in comparison with the kneading method described above. Therefore, in order to develop the color optical density equivalent to the density according to the kneading method, the photochromic compound is required to be dissolved thereinto with a high concentration. In the above case, such problems have remained as insufficiency of solubility and occurrence of precipitation during storage depending on a kind of the photochromic compound. Moreover, the layer in which the photochromism is developed is thin, and therefore durability of the photochromic compound has been deteriorated in several cases.
For example, Patent literature 4 discloses a method for coating a photochromic curable composition on a plastic lens by spin coating or the like to allow photocuring of the resulting material to form a photochromic coating layer (This lamination method is also called a coating method).
Moreover, Patent literature 5 discloses a method for forming a photochromic layer by securing a space between a plastic lens and a glass mold by using a member such as an elastomer gasket, a pressure-sensitive adhesive tape or a spacer, and flowing a photochromic curable composition into the space to allow polymerization curing thereof (hereinafter, also called two-step polymerization method).
Further, Patent literature 6 discloses a production method for a laminated sheet prepared by bonding a transparent carbonate sheet therewith by a polyurethane resin adhesive layer containing a photochromic compound (binder method).
Also in all the methods in Patent literature 4 to 6, however, the photochromism is developed in the thin layer in which the photochromic compound is blended. Therefore, when the photochromic compound having low solubility is used, the color optical density tends to be reduced, and further the durability of the photochromic compound has been also deteriorated in several cases.
Patent literature 7 discloses a lamination method for forming a photochromic coating layer by coating a photochromic urethane curable composition composed of polyol, isocyanate and the like on a plastic lens by spin coating or the like to allow thermal curing thereof. Also in this method, however, sufficient color optical density is unable to be secured.
As an art for solving the problems described above, Patent literature 8 discloses a photochromic composition consisting of a polyrotaxane having a composite molecular structure formed of an axle molecule and a plurality of cyclic molecules clathrating the axle molecule, and having a side chain containing a hydroxyl group in a part of the cyclic molecule, a polyisocyanate monomer and a photochromic compound. In the photochromic composition, both high mechanical strength caused by a urethane bond by incorporating the polyrotaxane thereinto, and excellent photochromism (color optical density and a color fading rate) by existence of a free space formed by bonding of the polyrotaxane to a part of the polyurethane are satisfied (see Patent literature 8).
Patent Literature
Patent literature 1: WO 2005/095493 A
Patent literature 2: WO 2012/176439 A
Patent literature 3: WO 2009/075388 A
Patent literature 4: WO 2011/125956 A
Patent literature 5: WO 2003/011967 A
Patent literature 6: WO 2013/099640 A
Patent literature 7: WO 2001/055269 A
Patent literature 8: WO 2015/068798 A
Patent literature 8 above describes evaluation results indicating a level having substantial no problem on moldability (optical strain and cloudiness). When an evaluation with higher accuracy is conducted, however, the moldability has become insufficient in several cases. Moreover, when various lens shapes have been evaluated in a similar manner, in particular, a problem of moldability has become significant in the case of a thick lens, and room for further improvement has remained.